Magnet construction



Jan. 17, 1939. G HALE ET AL 2,144,184

MAGNET CONSTRUCTION Filed Nov. 30, 1934 652/94 0 //AL .6 K. 1. 56077 INVENTORS Q5 wW M ATTORNEY.

Patented Jan. 17, 1939 UNITED STATES PATENT OFFICE Western Springs, 111., assign ors, by mesne assignments, to Magnet-O-Signs Corporation, a

corporation of Illinois Application November 30, 1934, Serial No. 755,306

Our invention relates to a method of constructing magnets of a small size to act as a supporting means for display letters or devices or toys formed of a plastic or other moulded material, or for the construction of magnets for any other use where high magnetic power in relation to the'mass or volume of the magnet is a requisite.

Our invention further relates to a combination of such magnets with plastic letters, devices or toys and a magnetic metallic plate for supporting and displaying such letters.

Other objects of our invention will appear and be described in the specification.

The novelty of our invention will be hereinafter more fully set forth and specifically pointed out in the claim.

In the accompanying drawing;

Fig. 1 is a side elevation of a magnet drawn four times natural size.

Fig. 2 is an end elevation of such a magnet.

Fig. 3 is a perspective view of the magnet shown in Figs. 1 and 2.

Fig. 4 is a reverse view of a figure 4 containing a magnet 3 and a magnet 4.

Fig. 5 is a perspective view of the figure 4 shown in Fig. 4. a

In Fig. l, the dimension 1" refers to the actual length of the magnet; the dimension L, shown by the dotted line, refers to the length of the magnet as discussed in this application, length referring to the distance from the center of one face to the center of the other along the dotted line; the dimension H refers to the height including the feet; dimension F refers to the width of the foot at the face of the magnet pole and the dimension B refers to width of the foot at its base; dimension T refers to the height of the magnet not taking into account the feet; in Fig. 2 the dimension W refers to the width of the magnet. D, which we term the diameter of the magnet and which appears in the formula below, is the diameter of a circle having an area equal to the cross sectional area of the magnet, determined from the equation to have the value producing small plastic tablets containing magnets of sufficient magnetic power to support the tablets permanently and firmly upon a plate of magnetic material. We have found that by maintaining certain dimensional proportions in magnets, the most efficient magnet in relation to its size or mass can be produced. In maintaining these proportions the maximum efilciency is attained, when using a high quality of cobalt magnet steel containing between 25% and 35% of cobalt, or precipitation hardening magnet ailoys, or other alloys of a magnetic quality equal to cobalt magnet steel.

We have found that if a dimensional relation is maintained between the length ofthe magnet, or L, and the magnets diameter, or D, taking into account certain properties of the magnet material hereafter referred to, the most emcient magnet will result.

We have further found that a specific relationship exists between the strength of the magnet, the dimensions of the magnet, and the magnetic properties of the magnet material, that is, the residual induction in gauss, represented in the art by the symbol Br, and the coercive force in oersteds, represented in the art by the symbol He. Both of these properties have been or can be specifically determined for any given magnet material. In producing a magnet of the desired maximum efiiciency, we follow the formula Following this formula will produce the strongest magnet possible from a given amount of material or in a magnet of a given length, or a desired diameter. Assume that it is necessary to design magnets of sufiicient power to support a plastic figure four, one and one-half inches high. The available material is Honda magnet steel containing 35% cobalt having a B1: of 10,000 in gauss and an He of 225 in oersteds. If the practicable limit for the magnets over all length, or L is using the formula, the other dimensions of the magnet should be .75" H. Twat This would give a diameter of- .09 inch.

While in the laboratory, the foregoing formula produces the best result, in practice, particularly in the production of very small magnets, a small variation from the dimensions obtained from the formula will still very closely approximate the results obtained from following the formulae:- actly.

The foregoing formula applies only to a straight bar magnet and does not take into account the feet, I and 2, Fig. 1 which are tapered from the width at the base, B, to the width at the face, F, a construction which adds to the strength and force of the magnet. There seems to be no precise formula to follow in constructing the taper oi the feet but we have determined that the dimension H, Fig. l, is substantially constant with the dimension W, Fig. 2, and the dimensions B and F, Fig. I, maintain the ratio of three to two.

Applying these magnets to our display method for letters, numbers, symbols or devices and the like, or to childrens toys formed of disassembled pieces or otherwise, we take a piece of moulded plastic material having from one to three magnets of the requisite strength positioned in the back of the piece, the feet of the magnets being either flush with the back, protruding therefrom toga desired length to set of! the piece of material from a magnetic plate, or recessed in the plastic. If permanent magnets of the necessary strength are used, the tablets can be attached indefinitely to a metal1ic plate and can be removed therefrom or rearranged as desired.

Having fully described our invention, we claim: A permanent magnet of cobalt magnet steel containing between 25-35 per cent. cobalt, of a shape adapted to be embedded in tablets for holding them against plates of ferro-magnetic material, having a length or diameter bearing a relationship to the other dimension conforming substantially to the formula, the product of length times the square root of the coercive force of the material used is equal to 1.25 times the diameter times the square root of the residual induction of the material used.

GERALD HALE. KENNETH L. SCOTT. 

